Polarization has to do with the direction of the light. Think of a white picket fence – the kind that has space between each board. The light can pass through the gaps int the fence but are blocked by the boards. That’s exactly what a polarizer does.
When you have two polarizers, you can rotate one of the ‘fences’ a quarter turn so that virtually no light can get through – only little bits here and there where the gaps line up. Most of the way is blocked, though, which is what happens when you rotate the two pairs of sunglasses. Your sunglasses are polarizing filters, meaning that they only let light of a certain direction in. The view through the sunglasses is a bit dimmer, as less photons reach your eyeball.
Polarizing sunglasses also reduce darken the sky, which gives you more contrast between light and dark, sharpening the images. Photographers use polarizing filters to cut out glaring reflections.
Materials:
- two pairs of polarized sunglasses
- tape (the 3/4″ glossy clear kind works best – watch second video below)
- window
[am4show have=’p8;p9;p11;p38;p92;p19;p46;p105;p89;’ guest_error=’Guest error message’ user_error=’User error message’ ]
Here’s what you do: Stack two pairs of sunglasses on top of each other and look through both sets of lenses… now rotate one pair a quarter turn (90o). The lenses should block the light completely at 90o and allow light to pass-through when aligned at 0o. These lenses allow some light to pass through but not all. When you rotate the lenses to 90o, you block out all visible light.
You use the “filter” principle in the kitchen. When you cook pasta, you use a filter (a strainer) to get the pasta out of the water. That’s what the sunglasses are doing – they are filtering out certain types of light. Rotating the lenses 90o to block out all light is like trying to strain your pasta with a mixing bowl. You don’t allow anything to pass through.
Astronomers use polarizing filters to look at the moon. Ever notice how bright the moon is during a full moon, and how dim it is near new moon? Using a rotating polarizing filter, astronomer can adjust the amount of light that enters into their eye.
Download Student Worksheet & Exercises
Advanced students: Download your Polarization lab here.
Exercises
- Why do you need two polarizers to block the light completely?
- How can you tell if your sunglasses are polarized if you only have one pair?
[/am4show]